The invention relates to a sensor for radiation pyrometric temperature determination of an object to be measured, especially under conditions of high ambient temperature in the interior of a dryer etc.
With such sensors a contact-free measurement of the surface temperature of an object to be measured, for example, of solid materials, compounds, and products, in hot air dryers and heat treatment devices is possible. With a plurality of sensors, arranged as close as possible to the surface to be measured, the determination of a spacial temperature profile over time of the material to be treated is possible. This, in addition to other process parameters, provides an important prerequisite for optimizing the process course with respect to economic considerations and quality control. Such heat treatment devices are used in the textile industry, paper industry, wood industry, furniture industry and also in the manufacture of sheet rock etc.
It is known to provide a radiation pyrometer external to the device and to observe through openings, i.e., a heat radiation-transmissive window, the object to be measured, respectively, its surface for measuring the temperature. Only when an optical and radiation-transmissive visual connection is provided, is the measurement of sufficient precision. However, when a relatively large distance exists between the object to be measured and the pyrometer, the measurement is considerably disrupted by radiation-absorbing gases, vapors, or aerosols. Further disturbing factors can be the emission degree of the object to be measured with respect to reflection of foreign radiation or, when using windows, their spectral absorption properties. The arrangement of radiation pyrometers requires the installation of a transverse air lock and of cooling devices for preventing condensation and sublimation effects and for heat protection of the pyrometer optics and pyrometer electronic devices. The use of a plurality of pyrometers, as is, for example, necessary for measuring a temperature profile, is therefore hardly economically justifiable because of the expenditure.
It is also known (Textilbetrieb 1981, Vol. 4, page 55), to arrange for the purpose of process control in belt dryers a plurality of simple temperature sensors, for example, in the form of thermoelements along the path adjacent to one another directly in slip contact on the belt, at a short distance thereto or within the exhaust gas stream. This allows a control of the temperature with respect to the temperature trend, however, the temperature course which is important for certain chemical, respectively, physical-chemical processes can not be determined with sufficient precision.
From German patent application 41 02 524 a sensor for radiation temperature measurement in the infrared spectral range is known which in the form of a miniature thermocolumn arrangement that is produced in thin layer technology. This sensor, however, does not withstand the temperatures present within the interior of a heat treatment device. Also, known resistance thermometers (German patent application 35 36 133) can not be used with sufficient precision in the range of high ambient temperature.
It is therefore an object of the invention to provide a sensor for radiation temperature measurement which allows for precise temperature measurement of an object to be measured even for high ambient temperatures in its direct vicinity.